1. Field of the Invention
The present invention relates to an apparatus for positioning a semiconductor wafer, and, in particular, to an apparatus for positioning a semiconductor wafer in which a pattern of circuits is formed.
2. Description of Background
Usually, a disk type of semiconductor wafer is subjected to a facing processing in which the side surface of the wafer is, for example, ground to a .SIGMA. structure or a tapered structure. That is, as shown in FIG. 1(a), the side surface 11A of a disk type of rotated wafer 11 is ground by a grindstone 12. In this case, the rotational axis 11B of the rotated wafer 11 must agree with the center 13A of a pattern of circuits 13 as shown in FIG. 1(b). However, the center 13A of the pattern of circuits 13 does not agree with the center of the wafer 11.
Therefore, the wafer 11 must be positioned to set the center 13A of the pattern of circuits 13 at the rotational axis 11B of the wafer 11.
A conventional apparatus for positioning a semiconductor wafer is shown in FIG. 2.
As shown in FIG. 2, a conventional apparatus 21 for positioning a semiconductor wafer comprises:
a wafer holder 22 for holding a disk type of wafer 23;
a positioning stage 24 for moving the wafer holder 22 to set the wafer 23 at a prescribed position, a reference point 25A being marked on the center of circuits 25 formed on the wafer 23 as shown in FIG. 3A; and
a microscope 26 for magnifying the wafer 23 to observe the real image of the circuits 25 formed on the wafer 23.
The positioning stage 24 comprises:
an X-axis stage 27 for moving the wafer 23 in an X-axis direction;
a Y-axis stage 28 for moving the wafer 23 in an Y-axis direction;
a .theta.-axis stage 29 for rotating the wafer 23 on an X-Y plane;
an X-axis adjuster 30 for adjusting the movement of the wafer 23 in the X-axis direction by turning a knob by hand;
an Y-axis adjuster 31 for adjusting the movement of the wafer 23 in the Y-axis direction by turning a knob by hand; and
an .theta.-axis adjuster 32 for adjusting the rotation of the wafer 23 on the X-Y plane by turning a knob by hand.
The microscope 26 comprises:
an objective 33 for facing the wafer 23 on the wafer holder 22; and
an eyepiece 34 with a cross shaped of adjusting lines 34 shown in FIG. 3A.
In the above configuration of the conventional apparatus 21, the wafer 23 is initially put on the wafer holder 22 so that the wafer 23 is fixed by evacuating the wafer holder 22 by a vacuum system. Thereafter, the microscope 26 is focused on the wafer 23 by an operator. At this time, the operator can observe the circuits 25 formed on the wafer 23 as shown in FIG. 3A.
Thereafter, the operator adjusts the X, Y, .theta.-axis adjusters 30, 31, 32 to position an intersection point 34A of the adjusting lines 34 at the reference point 25A marked on the center of circuits 25 as shown in FIG. 3B. At this time, the operator keeps to observe the circuits 25 through the microscope 26. After this adjustment, the operator can observe the circuits 25 formed on the wafer 23 as shown in FIG. 3B. That is, the reference point 25A marked on the center of circuits 25 agrees with the intersection point 34A of the adjusting lines 34.
Accordingly, a process for positioning the wafer 23 is completed by the above adjustment.
Thereafter, the wafer 23 is transferred to a next processing stage to implement the facing processing by moving a prescrived distance. Or, in cases where the positioning of the wafer 23 is required in a high precision, the processing stage such as the grindstone 12 for implementing the facing processing is transferred to the side of the wafer 23 so that the facing processing is implemented without transferring the wafer 23.
However, there are many drawbacks in the positioning process. That is, the adjustment for positioning the wafer 23 is implemented by hand so that the operator must engage in the positioning process for a long time. Therefore, the positioning process is troublesome.
In addition, the operator is subjected to the fatigue of the eyes because the operator must keep to observe the circuits 25 and the adjusting lines 34 with his eyes like saucers for a long time. Therefore, the productivity is decreased, and the quality of the semiconductor device manufactured by implementing the facing process deteriorates.
Moreover, in cases where the size of the circuits formed on the wafer 23 is changed because the dimensions of the wafer 23 is changed, the positioning allowance is changed. For example, the dimensions of the wafer 23 is changed from 6 inch to 4 inch, the positioning allowance is reduced. Therefore, the positioning are required in a higher precision. In this case, both the objective 33 and the eyepiece 34 of the microscope 26 must be changed for each size of wafer 23.
Further, because the operator must judge with his eyes whether or not the reference point 25A of the circuits 25 agrees with the intersection point 34A of the adjusting lines 34, the operator must turn the .theta.-axis adjuster 32 to easily make a judgment. That is, the operator must turn the three type of knobs.
Therefore, the improvement in the positioning process is strongly required.